This invention relates to semiconductor devices such as light emitting diodes. In particular, this invention relates to an apparatus for regulating the temperature of a light emitting diode.
The emission spectrum (in terms of both intensity and peak wavelength) of an LED is temperature dependent. In particular, it is the junction temperature of the LED that influences the emission spectrum. To achieve a stable light output from an LED, it is therefore necessary to regulate the temperature of the LED.
Traditionally, the junction temperature in the LED is measured directly or indirectly via a temperature sensor and a model to derive the junction temperature, and the LED is then operated (by adjusting the amplitude, frequency and/or duty cycle of the current passing through the LED) to react to any changes in LED temperature. Arrangements of this kind are complex, and require the provision of a control loop including at least a variable current supply and means for measuring the LED temperature.